The installation and maintenance of solar receivers is a major issue in the proper operation of tower solar power plants. The proper performance of these two operations guarantees optimal performances by the plant for as long as possible.
Several solutions based on the use of a crane exist in several fields: construction, wind energy, etc. In the solar field, and in particular in tower solar power plants, cranes are generally used in the construction, installation and assembly of solar receivers atop the tower.
In the case of the solar receivers of the cavity type (for example, Khi Solar One project in South Africa) or small external receivers, a large crane higher than the tower is installed in order to perform the assembly operations of the receiver. This is applicable in the case of installation atop the tower before commissioning. Once this installation is complete, the assembly tower is disassembled and the maintenance operations will be performed through access doors in the tower and in the receiver. The equipment is mounted atop the tower using a lifting device.
For the solar receiver of the external type, a solution with a crane mounted atop the tower has been developed by the company SolarReserve, California, USA. This solution was the subject of two patents that were filed in 2009 (U.S. Pat. No. 8,544,237 B2) and 2010 (US 2011/0297206 A1) in the USA and Spain.
The first of these patents presents a lifting method and a lifting system installed on a solar tower for replacing panels of the solar receiver. The system is made up of:                a guide track installed over the entire height of the tower, along which a receiving panel can be moved from the ground using a wheeled carriage moving by going up the track and by a first cable actuated by a winch situated at the apex of the tower;        a crane installed atop the receiver, which is in turn situated on the upper base of the tower, capable of rotating 360 degrees and attached to a second cable. Once the receiving panel is conveyed to the apex of the tower by the guide and lifting system described above, it is borne by the crane, which conveys it to the location provided for its positioning. Of course, the operations are done in reverse to disassemble a panel located on the receiver.        
The second patent, which is based on the first one, presents a method and system for replacing panels of a solar receiver external to the tower. The system is made up of:                a crane installed atop the tower to support the panel. The crane body can move horizontally and rotatably for example using a turntable, which allows it to access all of the panel locations;        a carriage with a support frame that maintains and transports the panel;        circular rails installed atop the tower, around the receiver, to guide the carriage.        
The panel replacement method consists of:                deploying the crane;        attaching and supporting the panel using the crane;        moving and depositing the panel on the carriage;        moving the carriage-panel assembly and passing the panel through an access hatch or positioning it using the crane.        
Although this solution is very interesting, it does not make it possible to:                transport large-size panels;        perform maintenance operations directly on the receiver.        
Document CN 203269405 U describes a crane intended to assemble side panels moving on concentric paths. This document is part of the general state of the art, since the crane is balanced by a central anchor.
Two other documents relate to the steelyard-lever scale system at the load. Document CN 201406267 U presents a system making it possible to handle a tool such as a lubrication pump with a certain degree of freedom provided by the steelyard-lever scale system (orifices for placing weights are provided in the median part of the beam of the scale). Document CN 104555715 A also presents an offset system for the load using a steelyard-lever scale. However, the scale remains horizontal throughout the entire maneuvering in both cases.
Lastly, in document FR 2 329 579 A1, the interest lies in assembling crane elements in the vertical and offset plane owing to an effect of the lever.